Carbonate polymers containing a salt of a crown complex as an ignition depressant

ABSTRACT

A polycarbonate such as bisphenol-A homopolycarbonate containing a small amount of a crown salt, e.g., an 18-crown ether (potassium fluoroborate), resists combustion upon exposure to a low temperature ignition source.

DESCRIPTION OF THE INVENTION

This invention relates to carbonate polymers containing additives which inhibit combustion upon exposure of the polycarbonates to low temperature ignition sources.

Polycarbonates derived from the reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives, such as phosgene, have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers and other carbonate polymers appear to be particularly suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are required.

Unfortunately, however, these polymers exhibit a brief but definite burning time when contacted with an open flame or comparable low temperature ignition source. Most importantly, as is often the case, the polycarbonates contain stabilizers and other additives which are often more combustible than the unmodified polycarbonate. As a result, the modified polycarbonate frequently exhibits substantially poorer resistance to combustion than does the unmodified polycarbonate.

In attempts to increase the combustion resistance of polycarbonates including modified forms thereof, it has been a common practice to employ monomeric phosphites, phosphoric acid esters, thiophosphoric acid esters containing halogenated alkyl radicals and halogenated organic compounds into the polycarbonate. However, in order to obtain any noticeable improvement in combustion resistance, these additives have been employed in such large quantities that they often adversely affect many of the desirable physical and mechanical properties of the polycarbonate.

More recently, for example, as taught in U.S. Pat. No. 3,919,167, various organosulfonate salts have been employed as fire retardant additives for the polycarbonates. While these materials do not have a substantial deleterious effect on the physical properties of the polycarbonate, they generally must be employed in concentrations of at least one weight percent based on the polycarbonate in order to obtain a material that does not exhibit flaming drips upon a combustion in accordance with Underwriters Lab Standard Test UL-94.

In view of the deficiencies of conventional fire retardant polycarbonate compositions, it would be highly desirable to provide a polycarbonate composition having improved resistance to burning when exposed to a low temperature ignition source.

SUMMARY OF THE INVENTION

The present invention is a polycarbonate composition comprising a carbonate polymer having dispersed therein a thermally stable salt of a crown complex (hereinafter this salt shall be called crown salt). The crown salt is present in an amount sufficient to retard combustion when the composition is exposed to a low temperature ignition source. Hereinafter, such composition shall be referred to as a fire retardant polycarbonate. The fire retardant polycarbonate of the present invention exhibits surprisingly high resistance to combustion and physical properties comparable to the carbonate polymer containing no crown salt.

The fire retardant polycarbonate of the present invention is suitably employed in most applications in which polycarbonates have been previously utilized. Applications of particular interest for the utilization of the fire retardant polycarbonates of this invention are as follows: automobile parts, e.g., air filters, fan housings, exterior components; housings for electrical motors, appliances, business and office equipment, photographic equipment, electrical switch boxes, electronic components, lighting and aircraft applications.

In general, such fire retardant polycarbonates are particularly useful in applications wherein the polycarbonate part is likely to be exposed to low temperature ignition sources.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The carbonate polymers employed in the present invention are advantageously aromatic carbonate polymers such as the trityl diol carbonates described in U.S. Pat. Nos. 3,036,036; 3,036,037; 3,036,038 and 3,036,039; polycarbonates of bis(ar-hydroxyphenyl) alkylidenes (often called bisphenol-A type diols) including their aromatically and aliphatically substituted derivatives such as disclosed in U.S. Pat. Nos. 2,999,835; 3,028,365 and 3,334,154; and carbonate polymers derived from other aromatic diols such as described in U.S. Pat. No. 3,169,121.

It is understood, of course, that the carbonate polymer may be derived from two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with a hydroxy or acid terminated polyester or with a dibasic acid in the event that a carbonate copolymer or interpolymer rather than a homopolymer is desired. Also suitable for the practice of this invention are blends of any one of the above carbonate polymers. Also included in the term "carbonate polymer" are the ester/carbonate copolymers of the types described in U.S. Pat. Nos. 3,169,121; 4,105,633; 4,156,069 and 4,287,787. Of the aforementioned carbonate polymers, the polycarbonates of bisphenol-A and derivatives, including copolycarbonates of bisphenol-A, are preferred. Methods for preparing carbonate polymers for use in the practice of this invention are well known. For example, several suitable methods are disclosed in the aforementioned patents which are hereby incorporated by reference in their entirety.

The crown salts employed in the practice of this invention are those salts having a cation that is a complex of a metal ion and a hetero macrocyclic compound (crown compound), examples of which compounds and methods for their preparation are described in U.S. Pat. Nos. 4,072,693; 4,142,020; 4,080,337; 4,104,275; 3,847,949; 3,987,061; 3,562,295; 3,687,978; 3,856,813 and 3,686,225, which are hereby incorporated by reference. In general, any hetero macrocyclic compound that forms a complex with an alkali metal ion, which complex is soluble in an organic solvent, is suitable for use in this invention. Of particular interest are salts wherein the macrocyclic component is a macrocyclic polyether or substituted macrocyclic polyether. Preferred examples of such polyethers are represented by the formula: ##STR1## wherein n is a whole number from 3 to 24, preferably from 6 to 12, most preferably 6, and A is a divalent radical such as alkylene, arylene, alkylene cycloalkylene or other hydrocarbylene or carbonyl alkylene provided that at least 4 of A moieties per molecule are alkylene, more preferably ethylene or propylene, most preferably ethylene. The remaining A moieties (i.e., those that are not alkylene) are preferably 1,2-phenylene ##STR2## or substituted 1,2-phenylene; 1,2-cyclohexylene or substituted 1,2-cyclohexylene, 1,2-xylylene ##STR3## 1,4-xylylene and substituted 1,2- and 1,4-xylylenes; carbonyl methylene ##STR4## carbonylethylenecarbonyl ##STR5## carbonyl methylenecarbonyl ##STR6## and substituted derivatives thereof such as carbonyl phenylmethylene carbonyl ##STR7## and the like wherein substituents include hydroxyl, halo, such as chloro and bromo, aryl, alkyl, cycloalkyl, etc. Examples of especially preferred hetero macrocyclic compounds are the 18-crown ethers such as ##STR8##

The heat-stable crown salts are those represented by the formula: ##STR9## wherein ##STR10## is a crown compound as defined before; M^(+m) is an alkali metal or alkaline earth metal, preferably an alkali metal, more preferably sodium or potassium, most preferably potassium; X^(-m) is a suitable counteranion, preferably one containing a plurality of halogen atoms such as BF₄ ⁻, TiF₆ ⁻², SbF₆ ⁻, SiF₆ ⁻² and ZrF₆ ⁻², most preferably BF₄ ⁻ ; r is the number of ligand positions available for complexing with a metal ion and m is the valence of the particular ion. The crown salts are readily prepared by mixing the appropriate metal salt with the desired crown compound using well-known procedures and conditions, e.g., as shown in U.S. Pat. No. 3,686,225.

By "heat stable" is meant that the crown salt can, without degradation, be combined with or compounded into the carbonate polymer in the desired quantities by melt mixing techniques in a mixing apparatus such as a thermoplastic extruder wherein the carbonate polymer is converted to a heat plastified state during the dispersion of crown salt into the polymer. Such heat stable salts also can withstand the thermal conditions normally occurring during molding operations wherein the mixture of carbonate polymer and crown salt is melt processed using a conventional molding technique such as injection molding. Typically, the temperatures normally existing during the aforementioned mixing and molding techniques are those which are sufficient to convert the carbonate polymer to a heat plastified state but not enough to cause thermal degradation of the polymer, e.g., usually within the range of from 300° to about 325° C.

The crown salts are employed in particulate or powder form wherein the average particle diameter is preferably less than 5 micrometers, most preferably less than 1 micrometer.

The fire retardant polycarbonate of the present invention is suitably prepared by combining the carbonate polymer with an effective amount of crown salt using any one of a variety of blending procedures conventionally employed for incorporating additives into carbonate polymer resins. For example, dry particulates of the carbonate polymer and the crown salt are preferably dry blended and the resulting dry blend extruded into the desired shape. Alternatively, a solution of the crown salt is sprayed onto a dry particulate of the carbonate polymer and then molded or extruded into the desired shape.

While any amount of crown salt that imparts to the polycarbonate an improved resistance to ignition and/or combustion is suitable, preferred amounts of the salt are in the range from about 0.001 to about 0.5, especially from about 0.01 to about 0.1, weight percent based on the weight of the polycarbonate.

In addition to the aforementioned crown salts, other additives may be included in the fire retardant polycarbonate of the present invention such as other fire retardant additives, fillers, pigments, dyes, antioxidants, stabilizers, ultraviolet light absorbers, mold release agents and other additives commonly employed in polycarbonate resin formulations.

The following examples are given to further illustrate the invention and should not be construed as limiting its scope. In the following examples, all parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1

To a 3000-g sample of a homopolycarbonate of bisphenol-A, having a weight average molecular weight (Mw) of 32,000 as determined by gel permeation chromatography and sold under the trade name, Merlon M50F-1000 by Mobay Chemical, in the form of pellets [0.32 cm (dia)×0.32 cm (length)] is added 0.3 g of 18-crown-KBF₄ : ##STR11## in the form of a dry powder.

The blend is then dried at 250° F. for 4 hours and extruded and repelletized in a single screw extruder equipped with a static mixer and operating at 525° F. The extruded pellets are redried at 250° F. for up to 4 hours. These redried pellets are molded into test bars (12.7 cm×1.27 cm×0.32 cm) using a screw type injection molding unit wherein the molding temperature is 575° F. The injection molded bars are tested for combustibility (oxygen index and fire retardance). The results of these tests (Sample No. 1) are reported in Table I.

For the purposes of comparison, additional blends (Sample Nos. 2-4) are prepared using different amounts of the crown salt. These blends are also tested and the results are reported in Table I. In addition, several samples (Sample Nos. 5-12) are similarly prepared and tested using different amounts of the following crown salts: ##STR12## Also recorded in Table I are the combustibility properties of a control sample (Sample No. C) employing no fire retardant additive.

                  TABLE I                                                          ______________________________________                                                       O.sub.2                                                                               Flame Retardance (3)                                      Sample                                                                               Crown Salt (1)                                                                               Index (2)                                                                               Flame Time,                                       No.   Type    Amount %  % O.sub.2                                                                             Sec.     Rating                                 ______________________________________                                         1     A       0.01      33.0   5.8      V-2, V-2                               2     A       0.05      36.6   4.9      V-2, V-2                               3     A       0.10      36.2   5.6      V-0, V-1                               4     A       0.02      33.0   6.7      V-1, V-2                               5     B       0.01      33.0   5.9      V-2, V-2                               6     B       0.05      35.9   6.2      V-2, V-2                               7     B       0.10      37.2   5.7      V-1, V-2                               8     B       0.20      34.5   9.0      V-2, V-2                               9     C       0.01      35.2   8.1      V-1, V-2                               10    C       0.05      37.9   6.2      V-1, V-0                               11    C       0.10      36.6   6.4      V-1, V-1                               12    C       0.20      33.0   9.6      HB, V-2                                C*    None    --        29.0   22.1     HB, HB                                 ______________________________________                                          *Not an example of the invention                                               (1) A  18crown-KBF.sub.4                                                         B  dibenzo 18crown-KBF.sub.4                                                   C  dicyclohexo 18crown-KBF.sub.4                                             (2) Amount  weight percent based on polycarbonate                              (3) Underwriters Laboratories Standard Test UL94 as described in the 1980      Bulletin of Underwriters Laboratories                                    

As evidenced by the data shown in Table I, the crown salts impart significant fire retardance to carbonate polymers. 

What is claimed is:
 1. A composition comprising a carbonate polymer having dispersed therein a thermally stable crown salt having a cation that is a complex of an alkali metal or alkaline earth metal ion and a crown compound in an amount sufficient to retard combustion when the composition is exposed to a low temperature ignition source.
 2. The composition of claim 1 wherein the crown salt is represented by the formula: ##STR13## wherein each M^(+m) is individually alkali metal ion or alkaline earth metal ion; X^(-m) is a suitable counteranion for M^(+m), m is the valence of the particular ion, A is a divalent organic radical selected from the group consisting of alkylene, arylene, alkylene, cycloalkylene and carbonyl alkylene, n is a whole number from 3 to 24 and r is the number of ligand positions available for complexing with the metal ion.
 3. The composition of claim 2 wherein the crown salt is an 18-crown ether KBF₄ salt represented by one of the formulas: ##STR14## wherein each R is individually ##STR15##
 4. The composition of claim 3 wherein the crown salt is present in an amount from about 0.01 to about 0.2 weight percent of the carbonate polymer.
 5. The composition of claim 1 wherein the carbonate polymer is a carbonate homopolymer of bisphenol-A.
 6. The composition of claim 1 wherein the carbonate polymer is a copolyestercarbonate of bisphenol-A and terephthalic acid, isophthalic acid or a mixture thereof. 